Patent GB-592371-A (GB)
Title: Improvements relating to automatic telephone systems
IPC: H04Q3/00
Filed: 1945-05-04
Abstract: 592,371. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., and LONG, D. P. May 4, 1945, No. 11441. [Class 40 (iv)] In a group selector which carries traffic represented by either of two distinctive digits the outlet groups are marked over one or other of a pair of markers, depending on the receipt or non-receipt of a differentiating signal. A similar signal is transmitted to the subsequent switch and in each case may take the form of a potential applied temporarily to one of the speaking wires. As shown, the markers MA, MB are located in a control circuit common to two numerical groups of selectors, wipers 3, 5, 7 being associated with the group of which one selector is shown, and wipers 4, 6, 8 with the other group. Low resistance impulsing relay A operates over the preceding loop upon seizure, followed by release relay B and dialling relay C. Auxiliary relays BA, BB and coupling relay K are operated by B to connect the common control circuit to the seized selector and disconnect it from similar associated selectors. Discriminating relay P operates in series with A and locks, unless it is shortcircuited by an earth on the positive wire at the preceding selector, this being the discriminating signal, and if operated it operates PP followed by PA. PA then switches the operating circuit over from marking switch MA, appropriate to one digit value, to MB, appropriate to the other. If PP has been operated a circuit is completed over pp3 for drive magnet MU which moves its wipers to the preliminary contact position at the beginning of the dotted arcs, where a test relay T energizes over M1 and P1, in series with an opposing winding of PP which releases. If no discriminating signal is received the selector wipers remain on their normal contacts. Relay A responds to impulses and steps either MA or MB according to the condition of PA and at the end of the train C falls back to complete a drive circuit for magnet MU. Wiper switching is effected if necessary by energizing WS over MA5 or MB5, the appropriate contacts of which are strapped to terminal yz, and the selector drives to a free outlet in the group marked over marking wipers MA3 or MB3. On completion of the test circuit over the P and M arcs the operation of T stops the switch and energizes TA, which completes a circuit for switching relay H. This switches the line through and releases A followed by B, BA, BB and K, so as to free the common control circuit. The operated stepping switch now homes over its wiper 1. When a caller clears, earth is removed from wire p, so releasing H and completing the homing circuit of the selector. The arrangement shown allows a group to be divided, such as a group of twenty outlets being connected with ten outlets at the beginning of an even-numbered arc and ten at the end of the corresponding odd-numbered arc. During impulsing relay S energizes and connects earth to terminal sg and thence, when the digit switch has been set, over wiper 5 to operate relay WS. Searching commences when C falls back, but S is sufficiently slugged to hold itself, and therefore WS, while the first ten contacts are tested. It does, however, release before the fortieth contact is reached so that WS releases and this part of the search is done over the odd-numbered arc. If no free outlet is found the switch stops on the last contact of the arc in which search has been made. The test circuit includes relay LC, which disconnects relay A and substitutes high impedance relay AA, in which busy tone is induced over wire BT, while an overflow meter is operated over the positive speech wipers. Terminal s is connected to dead number contacts on marking bank 5 and if one of these is marked, WS is operated in series with S so that at the end of the unsuccessful search LC operates and NU tone is induced in the righthand winding of relay AA. Transmission of a discriminating signal to a succeeding selector is effected over appropriate connections to MA2 or MB2 when ta3 is up, earth then being connected to the positive wire to prevent operation of a relay, corresponding to P, in the following switching stage. Specification 378,585 is referred to.